The development of continuous production of high explosive materials, such as TNT, which are frequently transported in in process and in molten form in steam jacketed pipelines or ducts from one process location to another or from one building to another, has imposed the need for devices to minimize the chance of cumulative propagation of an accidental detonation event by attenuation of the detonation wave. Various means have been used in the prior art to interrupt a column of explosive material in order to reduce the supply of detonable material involved. Some prior art detonation trap devices accomplished this objective by insertion of a barrier or plug into an explosive carrying transmission line. Other prior art detonation trap devices reduce the supply of detonable material by separating the supply pipeline or column ends from each other by the creation of an air gap therebetween. Some prior art devices quench the detonation wave by the injection of a foreign material, such as water, which acts as an energy absorber and thus changes the state of the explosive fluid line. All of the abovementioned types of detonation traps require a minimum pipeline length to insure that the reignition of the downstream column does not take place. The problem with the aforementioned "active" detonation trap systems that effect the attenuation by the insertion of a barrier, the creation of an air gap, or by the introduction of a foreign material, is that the attenuation can only be accomplished by the rapid movement of hardware. In the aforementioned devices the existence of the detonation wave must first be detected and then the trap device activated. Usually such "active" detonation trap systems must utilize a control means to interpret a sensor signal, which then functions to generate a firing signal. The closure means and the signal processing means will require some finite time, therefore, the sensing means must generally be located some distance from the closure or barrier means in order to allow sufficient response time. The change of state type of detonation trap also has a similar time problem because material to be introduced into the explosive carrying line must be moved rapidly from a storage line to the transmission line in order to stop the cumulative self supporting reaction.
In contradistinction with the aforementioned prior detonation trap devices the present invention utilizes a critical size or confinement type detonation trap which does not involve any moving parts and therefore may be categorized as a "passive" type. The present invention tends not to propagate the chemical reaction causing the detonation wave because it reduces the ability of the system to concentrate enough energy at the point where the reaction is occurring and prevents the continuation and/or growth of the initial detonation wave. In a critical size detonation trap device, the rapid expansion of the reaction products, comprising essentially gaseous products, transports sufficient amount of energy away from the reaction zone to cause the reaction rate to decay whenever the size of the system is below a certain critical value. The response or flow of the explosive reaction products in transport lines generally depend upon the degree of confinement and the geometry of the transmission system, I have found that the critical size effect reflects the influence that confinement and geometry plays in propagation or decay. FIG. 1 is a plot illustrating how the critical size may vary as a function of a given confinement geometry. From FIG. 1 we see that the critical size can vary between the limits D.sub.u, which represents the unconfined case where the confinement is basically controlled by the inertia of the material itself, and the value D.sub.e, which represents the heavily confined case. Devices falling into the latter case would approach that of a constant volume system.
Other phenomena associated with the loss of energy from the reaction zone include such effects as the non-steady expansion resulting from a sudden enlargement of the explosive system which interacts with the confinement system in a complex way. An example of the local loss of energy from the reaction zone is the type of interaction which results in the phenomenon of low velocity detonation. In this latter type of reaction the initial state of the materials is momentarily altered. A similar effect occurs when there is prepressurization or dead pressing of the material such that it will not support the undesirable chemical reaction.